The present invention relates to a method of diagnosing leakage in an internal combustion engine common-rail injection system.
As is known, of the various problems that can occur in a common-rail injection system, the worst and most dangerous are one or more of the injectors jamming in the open position, and fuel leakage in the high-pressure fuel supply circuit, which results in fuel discharge in the form of a very fine spray.
On the one hand, high-pressure fuel leakage may cause a fire if the fuel spray should strike particularly hot engine surfaces; and, on the other, a jammed-open injector results in continuous fuel supply to the cylinders, in turn resulting not only in excessive fuel consumption but also in abnormal combustion characterized by pressure peaks and a considerable temperature increase in the cylinders.
Such defects can only be tolerated so long without causing serious damage to the engine, e.g. to the connecting rod, piston, or injector nozzles, and may immediately impair performance and safety of the vehicle.
To safeguard against such hazards, diagnostic units were proposed to detect fuel leakage in the injection system and to act on the injection system to cut off fuel supply to the injectors and so stop the engine immediately.
More specifically, such units operated by comparing the fuel pressure in the common rail or total fuel consumption of the engine with respective threshold values, and determined the presence or not of any hazardous situations accordingly.
Common-rail injection systems, however, are also subject to fuel leakage in the low-pressure fuel supply circuitxe2x80x94caused, for example, by fine cracks in the low-pressure conduitsxe2x80x94or to faulty low-pressure fuel supply circuit components preventing correct fuel supply to the high-pressure fuel supply circuit.
Such leakage and defects, however, are not as serious as a jammed-open injector or high-pressure fuel spray, by not immediately impairing engine performance or the safety of the vehicle, which, in such cases, in fact, can safely be driven at least to the nearest repair shop.
Known diagnostic units of the above type, however, were unable to distinguish between fuel leakage in the high-pressure fuel supply circuit and fuel leakage or faults in the low-pressure fuel supply circuit, so that, even in the case of minor, nonhazardous faults in the low-pressure fuel supply circuit, known diagnostic units immediately disabled the vehicle, thus causing considerable inconvenience to the driver, out of all proportion to the immediate danger involved.
One of the many solutions proposed to at least partly eliminate the above drawback is described in the Applicant""s European Patent Application EP-0786593, which proposes a fuel catch structure for determining fuel leakage from the high-pressure fuel supply conduits connecting the injectors to the common rail.
More specifically, the fuel catch structure comprises a number of sleeves made of elastomeric material, surrounding the injector supply conduits, and for catching any fuel leaking from the conduits; a catch header connected to and for collecting from the sleeves any fuel leaking from the injector supply conduits; a fluid sensor located at the bottom of the catch header to generate a leak signal indicating the presence of fuel in the catch header; and an alarm circuit connected to the fluid sensor to generate an alarm signal in the presence of fuel in the catch header.
Though advantageous in many respects, the above solution has several drawbacks preventing its advantages from being fully exploited.
More specifically, fuel leakage from the high-pressure supply conduits is determined using additional dedicated components not normally provided on the vehiclexe2x80x94such as the sleeves, catch header, fluid sensor, and alarm circuitxe2x80x94and which, besides costing money to manufacture or purchase and assemble, also call for regular servicing.
Moreover, the catch structure described above was only capable of determining one type of fault in the high-pressure fuel supply circuitxe2x80x94namely, fuel leakage from the high-pressure supply conduitsxe2x80x94so that any other faults in the high-pressure fuel supply circuit, such as a jammed-open injector, remained undiagnosed.
Another solution proposed to at least partly eliminate the above drawbacks is described in the Applicant""s European Patent Application EP-0785349, which proposes a diagnostic unit designed to determine the type of fault in the high-pressure fuel supply circuit, and in particular to distinguish between a jammed-open injector and a generic fault in the high-pressure fuel supply circuit.
More specifically, the diagnostic unit employs an accelerometer signal related to engine vibration intensity and generated by an accelerometer sensor on the engine block; and a position signal indicating the angular position of the drive shaft (engine angle). More specifically, the diagnostic unit compares the amplitude of the accelerometer signal with a first reference value; compares with a second reference value the engine angle value at which the amplitude of the accelerometer signal exceeds the first reference value; and determines a jammed-open injector condition according to the outcome of the two comparisons.
Though advantageous in many respects, the above solution has one drawback preventing its advantages from being fully exploited.
More specifically, the type of fault in the high-pressure fuel supply circuit is determined using an additional dedicated component not normally provided on the vehicle, i.e. the accelerometer sensor, which, besides costing money to manufacture or purchase and assemble, also calls for regular servicing.
To eliminate the above drawback, the Applicant""s European Patent Application EP-0785358 proposes a diagnostic unit designed to determine the type of fault in the fuel supply circuit as a whole, and in particular to distinguish between a jammed-open injector and a generic fault in the fuel supply circuit, without requiring the use of an additional accelerometer sensor not normally provided on the vehicle.
More specifically, the diagnostic unit first determines the presence of faults in the fuel supply circuit by comparing the fuel pressure in the common rail or the total fuel consumption of the engine with respective threshold values; and, in the event any faults are determined, distinguishes between a jammed-open injector and a generic fault in the fuel supply circuit on the basis of the engine torque, which is determined using a position and speed signal indicating the speed and angular position of the drive shaft and generated by a drive shaft speed and angular position detecting device already provided on the vehicle and substantially comprising a sound wheel fitted to the drive shaft, and an electromagnetic sensor associated with the sound wheel.
More specifically, if any faults are detected in the fuel supply circuit, the diagnostic unit reducesxe2x80x94in particular, cuts offxe2x80x94fuel injection into each engine cylinder; calculates, on the basis of said position and speed signal, the contribution of each cylinder to the value of the useful torque generated by the engine; compares each contribution with a respective reference value; and determines a jammed-open injector condition when at least one contribution is above the respective reference value, and a fault condition in the fuel supply circuit when all the contributions are below the respective reference values.
That is, if the diagnosed fuel leakage is caused by a fault in the fuel supply circuit, the reduction in the amount of fuel injected into the cylinders produces a corresponding reduction in the useful torque contribution of each cylinder; which reduction can easily be calculated as a function of the reduced injection time of each injector. Conversely, if the diagnosed fuel leakage is caused by a jammed-open injector, the reduction in the amount of fuel injected produces a smaller reduction in useful torque contributions than in the previous case, owing to the jammed-open injector feeding fuel continuously to the respective cylinder, which therefore shows no reduction in its contribution to the useful torque generated by the engine.
Though advantageous in many respects, the above solution has a minor drawback preventing its advantages from being fully exploited.
More specifically, a jammed-open injector is distinguished from a generic fault in the high-pressure supply circuit by comparing with a respective reference value the contribution of each cylinder to the useful torque generated by the engine. Computer simulation and road tests conducted by the Applicant, however, show fault diagnoses based on the above comparison to be unreliable in certain engine operating conditions. In particular, fault recognition problems may arise during transient operating states of the engine, e.g. during release.
It is therefore an object of the present invention to provide a leakage diagnosis method designed to eliminate the aforementioned drawbacks.
The present invention provides a method of diagnosing leakage in a high-pressure injection system of an internal combustion engine, which can comprise a number of cylinders. The injection system can comprise a number of injectors, each supplying high-pressure fuel to a respective cylinder of the engine, and a fuel supply circuit supplying fuel to the injectors. The diagnosis method can comprise the steps of: determining, for each of the cylinders, a quantity (ACi) related to the contribution of the cylinder to the torque generated by the engine; determining, for each of the cylinders, an unbalance index (ISi) indicating the unbalance of the quantity (ACi) related to the contribution of the cylinder to the torque generated by the engine with respect to the quantities (ACi) related to the contributions of the other cylinders to the torque generated by the engine; reducing, upon detection of a fault in the injection system, the amount of fuel injected into each of the cylinders; and distinguishing, for each of the injectors, between a jammed-open injector condition and a fault condition in the fuel supply circuit, on the basis of the variation in the unbalance index (ISi) of the respective cylinder following the fuel reduction.
In one embodiment of the diagnosis method, the quantity (ACi) related to the contribution of a cylinder to the torque generated by the engine can be the contribution of the cylinder to the angular acceleration of the engine.
In another embodiment of the diagnosis method, the unbalance index (ISi) associated with each of the cylinders can be related to the difference between the quantity (ACi) related to the contribution of the cylinder to the torque generated by the engine, and a mean value of the quantities (ACi) related to the contributions of the other cylinders to the torque generated by the engine.
In a further embodiment of the diagnosis method, the step of distinguishing, for each of the injectors, between a jammed-open injector condition and a fault condition in the fuel supply circuit can comprise the steps of: determining a differential unbalance index (Di) as a function of an unbalance index (ISi) prior to detection of the fault in the injection system, and of an unbalance index (ISi) following detection of the fault in the injection system; comparing the differential unbalance index (Di) with a threshold value (DTHi); determining a jammed-open injector condition when the differential unbalance index (Di) has a first predetermined relationship with the threshold value (DTHi); and determining a fault condition in the fuel supply circuit when the differential unbalance index (Di) does not have the first predetermined relationship with the threshold value (DTHi).
In one exemplary embodiment of the diagnosis method, the differential unbalance index (Di) can be related to the difference between the unbalance index (ISi) prior to detection of the fault in the injection system, and the unbalance index (ISi) following detection of the fault in the injection system.
In another exemplary embodiment of the diagnosis method, the unbalance index (ISi) following detection of the fault in the injection system can be calculated at the end of a transient operating state generated by the reduction in the amount of fuel injected into the cylinders.
In a further exemplary embodiment of the diagnosis method, the unbalance index (ISi) prior to detection of the fault in the injection system can be calculated immediately prior to detection of the fault in the injection system.
In a still further exemplary embodiment of the diagnosis method, the step of determining a jammed-open injector can comprise the step of determining whether the differential unbalance index (Di) is greater than the threshold value (DTHi).
In a still further exemplary embodiment of the diagnosis method, the step of determining a differential unbalance index (Di) can comprise the steps of: filtering the unbalance index (ISi) to generate a filtered unbalance index (ISFi); and determining the differential index (Di) as a function of an unbalance index (ISi) following detection of the fault in the injection system, and of a filtered unbalance index (ISFi) prior to detection of the fault in the injection system.
In another embodiment of the diagnosis method, the step of determining an unbalance index (ISi) for each of the cylinders can comprise the steps of: filtering the quantity (ACi) related to the contribution of the cylinder to the torque generated by the engine to generate a filtered quantity (ACFi) related to the contribution of the cylinder to the torque generated by the engine; and determining the unbalance index (ISi) as a function of the filtered quantity (ACFi).
In a further embodiment of the diagnosis method, the step of determining a fault in the injection system can comprise the steps of: determining the fuel pressure (PRAIL) of the fuel injected by the injectors; comparing the fuel pressure (PRAIL) with a threshold value (PMIN); and determining the fault in the injection system when the fuel pressure (PRAIL) has a first predetermined relationship with the threshold value (PMIN).
In an exemplary embodiment of the diagnosis method, the step of determining a fault in the injection system can comprise the step of determining whether the fuel pressure (PRAIL) is below the threshold value (PMIN).
In another embodiment of the diagnosis method, the fault in the injection system can be defined by a fuel leak in the injection system.
In a further embodiment of the diagnosis method, an engine can be provided which can comprise an exhaust gas recirculating system having a regulating valve. Additionally or alternatively, the diagnosis method can comprise the step of closing the regulating valve upon detection of the fault in the injection system.